Impact-absorbing pressure-sensitive adhesive sheet and method of producing the same

ABSTRACT

An impact-absorbing pressure-sensitive adhesive sheet according to an embodiment of the present invention includes an impact-absorbing pressure-sensitive adhesive layer including an impact-absorbing layer. A side surface of the impact-absorbing pressure-sensitive adhesive layer includes a tapered surface; and the tapered surface has a taper angle of 65° or more.

This application claims priority under 35 U.S.C. Section 119 to JapanesePatent Application No. 2006-211662 filed on Aug. 3, 2006, which isherein incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an impact-absorbing pressure-sensitiveadhesive sheet and to a method of producing the same. More specifically,the present invention relates to an impact-absorbing pressure-sensitiveadhesive sheet to be used for an image display apparatus such as aliquid crystal display apparatus and to a method of producing the same.

2. Description of the Related Art

A liquid crystal display apparatus must have polarizing plates arrangedon both sides of a liquid crystal panel based on its image formingsystem. The polarizing plates to be used are each generally prepared byattaching a protective film on both surfaces of a polarizer. Further,for optical compensation of a liquid crystal panel, an opticalcompensation film such as a retardation film may be arranged between thepolarizing plate and a glass substrate of the liquid crystal panel.

For preventing the glass substrate from being broken by external impact,there is disclosed arrangement of an impact-absorbing pressure-sensitiveadhesive layer on a viewer side of a glass substrate (see JP 2005-173462A). It is proposed that the impact-absorbing pressure-sensitive adhesivelayer is arranged on a viewer side of a polarizing plate or between thepolarizing plate and the glass substrate.

In a mobile device such as a cell phone, a protective layer formed of aplastic sheet or the like is generally provided on a viewer side of aliquid crystal display. Further, for preventing the liquid crystaldisplay from being broken by external impacts a space (air layer) isprovided between the liquid crystal display and the protective layer.However, there is a problem in that reflection occurs at an interfacebetween the protective layer and the air layer and an interface betweenthe air layer and the liquid crystal display to cause degradation inviewing properties. Thus, for assuring impact resistance, improving theviewing properties, and reducing a thickness of the plastic sheet(ultimately, mobile device), the impact-absorbing pressure-sensitiveadhesive layer described above is used instead of the air layer.

Meanwhile, the impact-absorbing pressure-sensitive adhesive layer isgenerally cut to match a size of an optical device to be applied to.However, the impact-absorbing pressure-sensitive adhesive layertypically has a thickness of several hundreds microns for obtainingsufficient impact resistance for practical use. Thus, there is a problemin that a cut surface may deform during cutting to cause adverse effectson display properties of an image display apparatus. Meanwhile, cuttingin high yield is desired.

SUMMARY OF THE INVENTION

The present invention has been made in view of solving conventionalproblems described above, and an object of the present invention istherefore to provide an impact-absorbing pressure-sensitive adhesivesheet causing no adverse effects on display properties and havingexcellent yield, and a method of producing the same.

An impact-absorbing pressure-sensitive adhesive sheet according to anembodiment of the present invention includes an impact-absorbingpressure-sensitive adhesive layer including an impact-absorbing layer. Aside surface of the impact-absorbing pressure-sensitive adhesive layerincludes a tapered surface; and the tapered surface has a taper angle of65° or more.

An impact-absorbing pressure-sensitive adhesive sheet according toanother embodiment of the present invention includes a substrate; and aplurality of impact-absorbing pressure-sensitive adhesive pieces eachincluding an impact-absorbing layer and provided on one side of thesubstrate. A side surface of each of the impact-absorbingpressure-sensitive adhesive pieces includes a tapered surface; and thetapered surface has a taper angle of 65° or more.

In one embodiment of the present invention, the plurality ofimpact-absorbing pressure-sensitive adhesive pieces are provided atcertain intervals on one side of the substrate; and a distance betweenside surface lower ends of the adjacent impact-absorbingpressure-sensitive adhesive pieces is 30 μm or more.

In another embodiment of the present invention, the impact-absorbinglayer has a thickness of 100 to 1,000 μm.

In still another embodiment of the present invention, theimpact-absorbing layer has a dynamic storage modulus G′ of 1×10⁷ Pa orless at 20° C.

According to another aspect of the present invention, a method ofproducing an impact-absorbing pressure-sensitive adhesive sheet isprovided. The method includes irradiating an impact-absorbingpressure-sensitive adhesive layer including an impact-absorbing layerwith laser light for cutting. A cut surface of the impact-absorbingpressure-sensitive adhesive layer includes a tapered surface; and thetapered surface has a taper angle of 65° or more.

In one embodiment of the present invention, a distance between cutsurfaces of the impact-absorbing pressure-sensitive adhesive layer is 30μm or more.

In another embodiment of the present invention, the laser light includeslight having a wavelength of at least one of 400 nm or less and/or 1.5μm or more.

Instill another embodiment of the present invention, the laser includesCO₂ laser.

In still another embodiment of the present invention, the method is forproducing an impact-absorbing pressure-sensitive adhesive sheetincluding: a substrate; and a plurality of impact-absorbingpressure-sensitive adhesive pieces each including an impact-absorbinglayer and provided on one side of the substrate.

The present invention can provide an impact-absorbing pressure-sensitiveadhesive sheet causing no adverse effects on display properties andhaving excellent yield.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIGS. 1A to 1C are each a schematic sectional view of animpact-absorbing pressure-sensitive adhesive sheet according to apreferred embodiment of the present invention; and

FIGS. 2A and 2B are each a schematic sectional view of animpact-absorbing pressure-sensitive adhesive sheet according to apreferred embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, preferred embodiments of the present invention will bedescribed, but the present invention is not limited to the embodiments.

A. Overall Structure

FIG. 1A is a schematic sectional view of an impact-absorbingpressure-sensitive adhesive sheet 100 according to a preferredembodiment of the present invention. The impact-absorbingpressure-sensitive adhesive sheet 100 is provided with animpact-absorbing pressure-sensitive adhesive layer 10 including animpact-absorbing layer. The impact-absorbing pressure-sensitive adhesivesheet 100 is further provided with: a first separator (substrate) 21arranged on one side of the impact-absorbing pressure-sensitive adhesivelayer 10; and a second separator 22 arranged on another side of theimpact-absorbing pressure-sensitive adhesive layer 10. FIG. 1B is aschematic sectional view of an impact-absorbing pressure-sensitiveadhesive sheet 200 according to another preferred embodiment of thepresent invention. The impact-absorbing pressure-sensitive adhesivesheet 200 is provided with the impact-absorbing pressure-sensitiveadhesive layer 10 including the impact-absorbing layer. Theimpact-absorbing pressure-sensitive adhesive sheet 200 is furtherprovided with: a first separator (substrate) 21 arranged on one side ofthe impact-absorbing pressure-sensitive adhesive layer 10; a secondseparator 22 arranged on another side of the impact-absorbingpressure-sensitive adhesive layer 10; a polarizing plate 30 arrangedbetween the impact-absorbing pressure-sensitive adhesive layer 10 andthe first separator 21; and a pressure-sensitive adhesive layer 40arranged between the polarizing plate 30 and the first separator 21.FIG. 1C is a schematic sectional view of an impact-absorbingpressure-sensitive adhesive sheet 300 according to still anotherpreferred embodiment of the present invention. The impact-absorbingpressure-sensitive adhesive sheet 300 is provided with theimpact-absorbing pressure-sensitive adhesive layer 10 including theimpact-absorbing layer. The impact-absorbing pressure-sensitive adhesivesheet 300 is further provided with: a separator (substrate) 20 arrangedon one side of the impact-absorbing pressure-sensitive adhesive layer10; the polarizing plate 30 arranged on another side of theimpact-absorbing pressure-sensitive adhesive layer 10; a support layer50 arranged between the impact-absorbing pressure-sensitive adhesivelayer 10 and the separator 20; and the pressure-sensitive adhesive layer40 arranged between the support layer 50 and the separator 20.

As shown in FIGS. 1A to 1C, the impact-absorbing pressure-sensitiveadhesive sheet of the present invention may further be provided with anyappropriate layers (films). The impact-absorbing pressure-sensitiveadhesive sheet of the present invention may further be provided with anyappropriate optical compensation layer although not shown. The kind,number, arrangement, and the like of such an optical compensation layermay appropriately be selected in accordance with the purpose. Further,in the embodiment as shown in FIG. 1C, for example, a surface treatedlayer may be provided on the polarizing plate 30 on a side having noimpact-absorbing pressure-sensitive adhesive layer 10 formed. Details ofrespective layers will be described below.

FIG. 2A is a schematic sectional view of an impact-absorbingpressure-sensitive adhesive sheet 400 according to another preferredembodiment of the present invention. The impact-absorbingpressure-sensitive adhesive sheet 400 is provided with: the firstseparator (substrate) 21; and impact-absorbing pressure-sensitiveadhesive pieces 10′, 10′, and 10′ provided on one side of the firstseparator 21. The impact-absorbing pressure-sensitive adhesive sheet 400is further provided with the second separator 22 arranged on eachimpact-absorbing pressure-sensitive adhesive piece 10′ on a side havingno first separator 21 arranged. FIG. 2B is a schematic sectional view ofan impact-absorbing pressure-sensitive adhesive sheet 500 according tostill another preferred embodiment of the present invention. Theimpact-absorbing pressure-sensitive adhesive sheet 500 is provided with:the first separator (substrate) 21; and the impact-absorbingpressure-sensitive adhesive pieces 10′, 10′, and 10′ provided on oneside of the first separator 21. The impact-absorbing pressure-sensitiveadhesive sheet 500 is further provided with: the second separator 22arranged on each impact-absorbing pressure-sensitive adhesive piece 10′on a side having no first separator 21 arranged; the polarizing plate 30arranged between the impact-absorbing pressure-sensitive adhesive piece10′ and the first separator 21; and the pressure-sensitive adhesivelayer 40 arranged between the polarizing plate 30 and the firstseparator 21. As shown in FIGS. 2A and 2B, the plurality ofimpact-absorbing pressure-sensitive adhesive pieces is provided on oneside of the substrate. Thus, excellent operability may be providedduring lamination to an optical device or the like, and excellent yieldmay be obtained.

B. Impact-absorbing Pressure-sensitive Adhesive Layer (Impact-absorbingPressure-sensitive Adhesive Pieces)

Side surfaces 11 and 11 of the impact-absorbing pressure-sensitiveadhesive layer 10 (impact-absorbing pressure-sensitive adhesive piece10′) are tapered surfaces. A taper angle of each of the taper surfacesis 65° or more, and is preferably as close to 90° as possible. Such astructure causes no adverse effects on display properties of an imagedisplay apparatus and may provide excellent yield. The taper angle ispreferably 75° or more, and more preferably 80° or more. Such a taperangle may provide excellent releasability from the separator(substrate). As a result, excellent operability during lamination to anoptical device may be provided. Note that in the specification of thepresent invention, the term “tapered surface” also includes the casewhere a side surface is substantially tapered state. The phrase“substantially tapered state” also includes the case where a sidesurface is not smooth within a range providing no adverse effects ondisplay properties of an image display apparatus. The term “taper angle”refers to θ shown in FIGS. 1A to 1C and 2A and 2B, and is a valuecalculated from an extended width x from an upper surface of a lowersurface of the impact-absorbing pressure-sensitive adhesive layer(impact-absorbing pressure-sensitive adhesive piece) and a thickness yof the impact-absorbing pressure-sensitive adhesive layer.

Preferably, the plurality of impact-absorbing pressure-adhesive pieces10′ are provided on one side of the substrate 21 at certain intervals. Aspacing (distance between the side surface 11 and the side surface 11)between the adjacent impact-absorbing pressure-sensitive adhesive pieces10′ and 10′ may be set to any appropriate value in accordance with astructure of the impact-absorbing pressure-sensitive adhesive sheet orthe like. A distance L1 between a side surface upper end 11 a and a sidesurface upper end 11 a is preferably 70 μm or more, more preferably 90to 230 μm, and particularly preferably 110 to 170 μm. A distance L2between a side surface lower end 11 b and a side surface lower end 11 bis preferably 30 μm or more, more preferably 30 to 120 μm, andparticularly preferably 30 to 60 μm. The spacings between the adjacentimpact-absorbing pressure-sensitive adhesive pieces are adjusted withinthe above ranges. Thus, excellent releasability from the substrate maybe provided, and excellent operability during lamination to an opticaldevice may be provided. Further, re-adhesion of the side surfaces of theadjacent impact-absorbing pressure-sensitive adhesive layer may beprevented, the tapered surfaces are favorably maintained, and excellentdisplay properties of an image display apparatus maybe provided.Meanwhile, excellent yield may be obtained.

Note that in the embodiment shown in FIG. 2A, a distance L3 between sidesurface upper ends 22 a of the adjacent second separators 22 ispreferably 80 μm or more, more preferably 100 to 350 μm, andparticularly preferably 120 to 310 μm. Further, in the embodiment shownin FIG. 2B, a distance L4 between side surface upper ends 22 a of theadjacent second separators 22 is preferably 80 μm or more, morepreferably 100 to 410 μm, and particularly preferably 120 to 370 μm.Further, a distance L5 between side surface lower ends 40 a of theadjacent pressure-sensitive adhesive layers 40 is preferably 30 μm ormore, more preferably 30 to 100 μm, and particularly preferably 30 to 50μm.

The side surface 11 of the impact-absorbing pressure-sensitive adhesivepiece 10′ is a tapered surface and satisfies the above taper angle, andthe spacing between the adjacent impact-absorbing pressure-sensitiveadhesive pieces 10′ and 10′ satisfies the above ranges. Thus,releasability may be remarkably improved. As a result, remarkablyexcellent operability may be obtained.

The impact-absorbing pressure-sensitive adhesive layer 10(impact-absorbing pressure-sensitive adhesive piece 10′) includes atleast an impact-absorbing layer. Hereinafter, the impact-absorbing layerwill be described.

B-1 Impact-absorbing Layer

The impact-absorbing layer mentioned above can be made of anyappropriate adhesive. Specific examples thereof include acrylicadhesives containing a (meth)acrylic polymer. Examples of monomer thatforms the (meth)acrylic polymer include alkyl(meth)acrylate. Specificexamples of alkyl(meth)acrylate include butyl(meth)acrylate,isobutyl(meth)acrylate, hexyl(meth)acrylate, 2-ethylhexyl(meth)acrylate,isooctyl(meth)acrylate, isononyl(meth)acrylate, allyl(meth)acrylate,lauryl(meth)acrylate, and stearyl(meth)acrylate.

The above-mentioned (meth)acrylic polymer is preferably obtained fromcopolymerization between alkyl(meth)acrylate and hydroxylgroup-containing monomer. Specific examples of hydroxyl group-containingmonomers include hydroxyalkyl(meth)acrylate such as2-hydroxyethyl(meth)acrylate, 2-hydroxypropyl(meth)acrylate,4-hydroxybutyl(meth)acrylate, 6-hydroxyhexyl(meth)acrylate,8-hydroxyoctyl(meth)acrylate, 10-hydroxydecyl(meth)acrylate,12-hydroxylauryl(meth)acrylate and(4-hydroxymethylcyclohexyl)-methylacrylate, polyethyleneglycol(meth)acrylate, and polypropylene glycol(meth)acrylate.

Any appropriate polymerization initiator can be used in polymerizationof the above-mentioned (meth)acrylic polymer. Specific examples ofpolymerization initiator include acetophenon-based photopolymerizationinitiators such as 4-(2-hydroxyethoxy)phenyl(2-hydroxy-2-propyl)ketone,α-hydroxy-α,α′-dimethylacetophenon, methoxyacetophenon,2,2-dimethoxy-2-phenylacetophenon, 2,2-diethoxyacetophenon,1-hydroxycyclohexylphenylketone, and2-methyl-1-[4-(methylthio)-phenyl]-2-morphorinopropane-1.

Cross-linking agent may be added in polymerization described above.Examples of cross-linking agent include polyfunctional(meth)acrylate.Specific examples of polyfunctional(meth)acrylate include hexanedioldi(meth)acrylate, (poly)ethylene glycol di(meth)acrylate,(poly)propylene glycol di(meth)acrylate, neopentyl glycoldi(meth)acrylate, pentaerythritol di(meth)acrylate, trimethylolpropanetri(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritolhexa(meth)acrylate, epoxy(meth)acrylate, polyester(meth)acrylate, andurethane(meth)acrylate.

A dynamic storage modulus G′ of the impact-absorbing layer at 20° C. ispreferably 1×10⁷ Pa or less, and more preferably 1×10³ to 7×10⁶ Pabecause excellent impact-absorbing ability may be provided.

A thickness of the impact-absorbing layer is preferably 100 to 1,000 μm,and more preferably 100 to 600 μm. A thickness thereof of less than 100μm may not provide sufficient impact-absorbing ability, and a thicknessthereof of more than 1,000 μm may cause problems in viewing properties.

Note that the impact-absorbing layer may employ a pressure-sensitiveadhesive layer for prevention of cracks in glass described in forexample JP 2005-173462 A, which is herein incorporated by reference.

B-2. Other Layers

The impact-absorbing pressure-sensitive adhesive layer (impact-absorbingpressure-sensitive adhesive piece) may further include an undercoatlayer arranged on one surface or both surfaces of the impact-absorbinglayer. The undercoat layer is provided, to thereby improvepressure-sensitive adhesive properties of the impact-absorbing layer toan adherend. A material used for forming the undercoat layer may employany appropriate material. As a specific example, description will begiven of an undercoat layer formed by crosslinking a pressure-sensitiveadhesive composition.

The pressure-sensitive adhesive composition preferably contains a(meth)acrylic polymer and an isocyanate-based compound. Similarly to thesection B-1 described above, the (meth)acrylic polymer refers to apolymer or a copolymer synthesized from an acrylate-based monomer and/ora methacrylate-based monomer (referred to as (meth)acrylate in thespecification of the present invention). In the case where the(meth)acrylic polymer is a copolymer, an arrangement state of copolymermolecules is not particularly limited. The copolymer may be a randomcopolymer, a block copolymer, or a graft copolymer. A preferredmolecular arrangement state is a random copolymer.

The (meth)acrylic polymer is obtained through homopolymerization orcopolymerization of alkyl (meth)acrylate. An alkyl group ofalkyl(meth)actylate may be linear, branched, or cyclic. The number ofcarbon atoms in the alkyl group of alkyl(meth)acrylate is preferablyabout 1 to 18, and more preferably 1 to 10.

Specific examples of the above-mentioned alkyl(meth)acrylate includemethyl(meth)acrylate, ethyl(meth)acrylate, propyl(meth)acrylate,n-butyl(meth)acrylate, iso-butyl(meth)acrylate, t-butyl(meth)acrylate,n-pentyl(meth)acrylate, iso-pentyl(meth)acrylate, n-hexyl(meth)acrylate,iso-hexyl(meth)acrylate, n-heptyl(meth)acrylate,iso-heptyl(meth)acrylate, 2-ethylhexyl(meth)acrylate,n-octyl(meth)acrylate, iso-octyl(meth)acrylate, n-nonyl(meth)acrylate,iso-nonyl(meth)acrylate, lauryl(meth)acrylate, stearyl(meth)acrylate,and cyclohexyl(meth)acrylate. They may be used alone or in combination.When using them in combination, alkyl group having average of 3 to 9carbon atoms is preferable for the alkyl(meth)acrylate.

The (meth)acrylic polymer may be a copolymer of alkyl(meth)acrylate andhydroxyl group-containing (meth)acrylate. In this case, the number ofcarbon atoms in the alkyl group of alkyl(meth)acrylate is preferably 1to 8, more preferably 2 to 8, particularly preferably 2 to 6, and mostpreferably 4 to 6. The alkyl group of alkyl(meth)acrylate may be linearor branched.

Specific examples of hydroxyl group-containing (meth)acrylate describedabove include 2-hydroxyethyl(meth)acrylate,3-hydroxypropyl(meth)acrylate, 2-hydroxypropyl(meth)acrylate,4-hydroxybutyl(meth)acrylate, 3-hydroxybutyl(meth)acrylate,2-hydroxybutyl(meth)acrylate, 5-hydroxypentyl(meth)acrylate,3-hydroxy-3-methylbutyl(meth)acrylate, 6-hydroxyhexyl(meth)acrylate,7-hydroxyheptyl(meth)acrylate, 8-hydroxyoctyl(meth)acrylate,10-hydroxydecyl(meth)acrylate, 12-hydroxylauryl(meth)acrylate, and(4-hydroxymethylcyclohexyl)-methylacrylate. They may be used alone or incombination.

The number of carbon atoms in a hydroxyalkyl group of hydroxylgroup-containing (meth)acrylate is preferably equal to or more than thenumber of carbon atoms in the alkyl group of alkyl(meth)acrylate. Thenumber of carbon atoms in the hydroxyalkyl group of hydroxylgroup-containing (meth)acrylate is preferably 2 to 8, and morepreferably 4 to 6. In this way, the number of carbon atoms is adjusted,to thereby provide excellent reactivity with an isocyanate-basedcompound described below. In the case where 4-hydroxybutyl(meth)acrylateis used as hydroxyl group-containing (meth)acrylate, for example,methyl(meth)acrylate, ethyl(meth)acrylate, propyl(meth)acrylate, orbutyl(meth)acrylate is preferably used as alkyl(meth)acrylate.

A copolymerization amount of hydroxyl group-containing (meth)acrylate ispreferably 0.01 to 10 mol %, more preferably 0.1 to 10 mol %,particularly preferably 0.2 to 5 mol %, andmost preferably 0.3 to 1.1mol %. A copolymerization amount with the above ranges may provide anundercoat layer having excellent adhesive property, durability, andstress relief property.

The (meth)acrylic polymer may be obtained through copolymerization withother components other than the above-mentioned alkyl(meth)acrylate andhydroxyl group-containing (meth)acrylate. The other components are notparticularly limited, but preferred examples thereof include(meth)acrylic acid, benzyl(meth)acrylate, methoxyethyl(meth)acrylate,ethoxymethyl(meth)acrylate, phenoxyethyl(meth)acrylate,(meth)acrylamide, vinyl acetate, and (meth)acrylonitrile. Acopolymerization amount of the other components is preferably 100 partsby weight or less, and more preferably 50 parts by weight or less withrespect to 100 parts by weight of alkyl(meth)acrylate.

A weight average molecular weight (Mw) of the (meth)acrylic polymer ispreferably 1,000,000 or more, more preferably 1,200,000 to 3,000,000,and particularly preferably 1,200,000 to 2,500,000.

Examples of the isocyanate-based compound described above includeisocyanate monomer such as 2,4-(or 2,6-)tolylene diisocyanate, xylylenediisocyanate, 1,3-bis(isocyanatemethyl)cyclohexane, hexamethylenediisocyanate, norbornene diisocyanate, chlorphenylene diisocyanate,tetramethylene diisocyanate, isophorone diisocyanate, diphenylmethanediisocyanate, trimethylolpropanexylene diisocyanate, and hydrogenateddiphenylmethane diisocyanate; adduct isocyanate compounds obtained byaddition of polyalchohol such as trimethylolpropane to thoseisocyanatemonomer; isocyanurate compound; biuret compounds; and urethaneprepolymer-type isocyanates obtained by addition reaction of anyappropriate polyetherpolyol, polyesterpolyol, acrylpolyol,polybutadienepolyol, polyisoprenepolyol, or the like. They may be usedalone or in combination.

The isocyanate-based compound may employ a commercially availableproduct as it is. Examples of the commercially availableisocyanate-based compound include: Takenate series (trade names “D-110N,500, 600, 700, etc.”) available from Mitsui Takeda Chemicals, Inc.; andCoronate series (trade names “L, MR, EH, HL, etc.”, for example)available from Nippon Polyurethane Industry Co., Ltd.).

A mixing amount of the isocyanate-based compound may be set to anyappropriate amount in accordance with the purpose. For example, themixing amount thereof is preferably 0.1 to 1.5 parts by weight, morepreferably 0.3 to 1.0 part by weight, and particularly preferably 0.4 to0.8 part by weight with respect to 100 parts by weight of the(meth)acrylic polymer. The mixing amount of the isocyanate-basedcompound is adjusted within the above ranges, to thereby provideappropriate stress relief property and excellent heat stability.Further, favorable adhesive property may be provided even in a harsh(high temperature and high humidity) environment.

The pressure-sensitive adhesive composition may further contain variousadditives without departing from the purpose of the present invention.Examples of the additives include a plasticizer, a heat stabilizer, aphoto stabilizer, a lubricant, an antioxidant, a UV absorber, a flameretardant, a colorant, an antistatic agent, a compatibilizing agent, acrosslinking agent, a coupling agent, a thickener, and a pigment.

A mixing amount of the other additives may be set to any appropriateamount in accordance with the purpose. The mixing amount thereof ispreferably more than 0 and 5 parts by weight or less with respect to 100parts by weight of the (meth)acrylic polymer.

A thickness of the undercoat layer may be set to any appropriate value.The thickness thereof is preferably 1 to 50 μm, more preferably 10 to 30μm, and particularly preferably 20 to 25 μm.

C. Polarizing Plate

The polarizing plate 30 typically includes a polarizer and a protectivefilm arranged on at least one side of the polarizer.

C-1. Polarizer

Any appropriate polarizer may be employed as the above-mentionedpolarizer in accordance with the purpose. Examples thereof include: afilm prepared by adsorbing a dichromatic substance such as iodine or adichromatic dye on a hydrophilic polymer film such as a polyvinylalcohol-based film, a partially formalized polyvinyl alcohol-based film,or a partially saponified ethylene/vinyl acetate copolymer-based filmand uniaxially stretching the film; and a polyene-based oriented filmsuch as a dehydrated product of a polyvinyl alcohol-based film or adechlorinated product of a polyvinyl chloride-based film. Of those, apolarizer prepared by adsorbing a dichromatic substance such as iodineon a polyvinyl alcohol-based film and uniaxially stretching the film isparticularly preferable because of high polarized dichromaticity. Athickness of the polarizer is not particularly limited, but is generallyabout 5 to 80 μm.

The polarizer prepared by adsorbing iodine on a polyvinyl alcohol-basedfilm and uniaxially stretching the film may be produced by, for example:immersing a polyvinyl alcohol-based film in an aqueous solution ofiodine for coloring; and stretching the film to a 3 to 7 times length ofthe original length. The aqueous solution may contain boric acid, zincsulfate, zinc chloride, or the like as required, or the polyvinylalcohol-based film may be immersed in an aqueous solution of potassiumiodide or the like. Further, the polyvinyl alcohol-based film may beimmersed and washed in water before coloring as required. Washing thepolyvinyl alcohol-based film with water not only allows removal ofcontamination on a film surface or washing away of an antiblockingagent, but also provides an effect of preventing nonuniformity such asuneven coloring by swelling of the polyvinyl alcohol-based film. Thestretching of the film may be performed after coloring of the film withiodine, performed during coloring of the film, or performed followed bycoloring of the film with iodine. The stretching may be performed in anaqueous solution of boric acid or potassium iodide, or in a water bath.

C-2. Protective Film

Any appropriate film, which can be used as a protective film for apolarizing plate, may be employed as the above-mentioned protectivefilm. Specific examples of a material used as a main component of thefilm include transparent resins such as a cellulose-based resin such astriacetylcellulose (TAC), a polyester-based resin, a polyvinylalcohol-based resin, a polycarbonate-based resin, a polyamide-basedresin, a polyimide-based resin, a polyether sulfone-based resin, apolysulfone-based resin, a polystyrene-based resin, apolynorbornene-based resin, a polyolefin-based resin, an acrylic resin,and an acetate-based resin. Another example thereof includesthermosetting resin or UV-curing resin such as an acrylic,urethane-based, acrylic urethane-based, epoxy-based, or silicone-based.Still another example thereof includes a glassy polymer such as asiloxane-based polymer. Further, a polymer film described in JP2001-343529 A (WO 01/37007) may also be used. To be specific, the filmis formed of a resin composition containing a thermoplastic resin havinga substituted or unsubstituted imide group on a side chain, and athermoplastic resin having a substituted or unsubstituted phenyl groupand a nitrile group on a side chain. A specific example thereof includesa resin composition containing an alternate copolymer of isobutene andN-methylmaleimide, and an acrylonitrile/styrene copolymer. The polymerfilm may be an extruded product of the above-mentioned resincomposition, for example. Of those, TAC, a polyimide-based resin, apolyvinyl alcohol-based resin and a glassy polymer are preferable, andTAC is more preferable.

It is preferable that the protective film be transparent and have nocolor. To be specific, the protective film has a thickness retardationof preferably −90 nm to +90 nm, more preferably −80 nm to +80 nm, andmost preferably −70 nm to +70 nm.

The protective film has any appropriate thickness direction as long asthe preferable thickness direction retardation can be obtained. To bespecific, the thickness of the protective film is preferably 5 mm orless, more preferably 1 mm or less, further more preferably 1 to 500 μm,and most preferably 5 to 150 μm.

The lamination of the polarizer and the protective film may be conductedthrough any appropriate pressure-sensitive adhesive layer or adhesivelayer.

For example, in FIG. 1C, the protective film to be provided above (on aside having no impact-absorbing pressure-sensitive adhesive layer 10formed) the polarizer may be provided with a surface treated layer asrequired. Specific examples of the surface treated layer include a hardcoat treated layer, an antireflection treated layer, an anti-stickingtreated layer, and an anti-glare treated layer.

D. Support Layer

The support layer 50 may typically be formed of a plastic film. Thesupport layer may be a monolayer of a plastic film, or a laminate ofplastic films. The plastic film may be formed of any appropriatematerial to be used as an optical film. Specific examples of thematerial include a norbornene-based resin, a polycarbonate-based resin,a cellulose-based resin, a (meth)acrylic resin, a polyester-based resin,and a nylon-based resin. Note that the support layer may be formed of aplastic film subjected to stretching treatment.

A dynamic storage modulus G′ of the support layer at 20° C. ispreferably 2×10⁸ Pa or more, more preferably 2×10⁸ Pa to 1×10¹¹ Pa, andparticularly preferably 5×10⁸ Pa to 1×10¹⁰ Pa. The support layer hassuch a dynamic storage modulus G′, and thus may have excellentself-supporting property. As a result, a polarizing plate provided withan impact-absorbing pressure-sensitive adhesive layer having excellentrework property and capable of effectively suppressing formation ofbubbles may be obtained.

A thickness of the support layer may be set to any appropriate value.The thickness thereof is preferably 5 to 500 μm, more preferably 10 to200 μm, and particularly preferably 10 to 100 μm. The support layer hassuch a thickness, and thus may have excellent self-supporting property.As a result, a polarizing plate provided with an impact-absorbingpressure-sensitive adhesive layer having excellent rework property andcapable of effectively suppressing formation of bubbles may be obtained.

The support layer may be optically isotropic or optically anisotropic(birefringent). In the case where the support layer has opticalisotropic property, the polarizing plate provided with animpact-absorbing pressure-sensitive adhesive layer to be obtained may beused without providing substantial effects on display properties of aliquid crystal display apparatus. In the case where the support layerhas optical anisotropic property, the support layer may also serve as anoptical compensation layer. In the case where the support layer hasoptical anisotropic property, optical properties (such as Δnd and Rth)may appropriately be set in accordance with drive mode and the like of aliquid crystal cell to be compensated. Note that in the specification ofthe present invention, the phrase “has optical isotropic property”includes the case where the support layer has substantial opticalisotropic property. The phrase “has substantial optical isotropicproperty” refers to the case where Δnd is less than 10 nm and anabsolute value of Rth is less than 10 nm.

E. Pressure-sensitive Adhesive Layer

A material used for forming the pressure-sensitive adhesive layer 40 mayemploy any appropriate pressure-sensitive adhesive. A specific examplethereof is the undercoat layer described in the above section B-2.

F. Separator (Substrate)

The separators (substrates) 20, 21, and 22 each typically include asupporting substrate, and a releasability-provided layer arranged on atleast one side (the side having the impact-absorbing pressure-sensitiveadhesive layer arranged) of the supporting substrate. The kind andapplication amount of a release agent used for forming thereleasability-provided layer may appropriately be selected, to therebyeasily adjust peel force of the separator.

The supporting substrate may employ any appropriate plastic film. Thesupporting substrate may be formed of a monolayer of a plastic film, ora laminate of plastic films. The plastic film may be formed of anyappropriate material as long as it is capable of exerting functions ofthe separator. Specific examples thereof include: nylons; ahalogen-containing polymer such as polyvinyl chloride; polyolefins suchas polyethylene and polypropylene; and polyesters such as polyethyleneterephthalate (PET). Of those, a polyester film is preferred from aviewpoint of punching workability or the like. Further, a material usedfor the supporting substrate preferably contains no component serving asa catalytic poison to a releasability-provided layer (such as a siliconeresin) Note that a surface of the supporting substrate may be subjectedto metal evaporation.

The releasability-provided layer may be formed of any appropriaterelease agent. Specific examples thereof include: a silicone-basedrelease agent such as a condensation-type, addition-type, etc.thermosetting silicone-based release agent; a radiation-curablesilicone-based release agent cured by UV light, electron beam, or thelike; a fluorine-based release agent containing an acrylic copolymerobtained through polymerization of a fluorine-containing ester of(meth)acrylic acid, an alkyl ester of (meth)acrylic acid having an alkylgroup of 8 or less carbon atoms, and the like; and a long-chainalkyl-based release agent containing an alkyl-based copolymer obtainedthrough polymerization of an alkyl ester of (meth)acrylic acid having along-chain alkyl group of 12 to 22 carbon atoms, an alkyl ester of(meth)acrylic acid having an alkyl group of 8 or less carbon atoms, andthe like (JP 29-3144 B, JP 29-7333 B). Of those, a silicone-basedrelease agent is preferred.

The releasability-provided layer may employ a release layer described infor example JP 2004-346093 A, which is herein incorporated by reference.

A thickness of the separator is typically about 15 to 100 μm, andpreferably about 30 to 100 μm.

G. Production Method

A method of producing an impact-absorbing pressure-sensitive adhesivesheet of the present invention includes a step of irradiating animpact-absorbing pressure-sensitive adhesive layer including animpact-absorbing layer with laser light for cutting. A typicallyemployed method involves: producing a laminate by laminating animpact-absorbing pressure-sensitive adhesive layer and desiredrespective layers (films) described above; and irradiating the laminatewith laser light (by laser ablation or the like) for cutting. Thelamination order and lamination method for the respective layers (films)may employ any appropriate method. Hereinafter, the production methodwill be described more specifically.

The impact-absorbing pressure-sensitive adhesive sheet as shown in FIG.2A can be obtained by: producing a laminate by laminating a firstseparator (substrate), an impact-absorbing pressure-sensitive adhesivelayer, and a second separator in the order given; and irradiating thelaminate from a side having no substrate arranged (side of the secondseparator) with laser light for cutting the laminate to the substrate(half cut). The impact-absorbing pressure-sensitive adhesive sheet asshown in FIG. 2B can be obtained by: producing a laminate by laminatinga first separator (substrate), a pressure-sensitive adhesive layer, apolarizing plate, an impact-absorbing pressure-sensitive adhesive layer,and a second separator in the order given; and irradiating the laminatefrom a side having no substrate arranged (side of the second separator)with laser light for cutting the laminate to the substrate (half cut).Impact-absorbing pressure-sensitive adhesive sheets as shown in FIGS. 1Aand 1B can be obtained by further cutting the impact-absorbingpressure-sensitive adhesive sheets shown in FIGS. 2A and 2B,respectively. That is, the impact-absorbing pressure-sensitive adhesivesheets as shown in FIGS. 1A and 1B can be obtained by cutting parts ofthe first separator (substrate) 21 having no impact-absorbingpressure-sensitive adhesive piece 10′ formed. A cutting method of thefirst separator (substrate) 21 may employ any appropriate method.

The impact-absorbing pressure-sensitive adhesive sheet as shown in FIG.1C can be obtained by: producing a laminate by laminating a separator, apressure-sensitive adhesive layer, a support layer, an impact-absorbingpressure-sensitive adhesive layer, and a polarizing plate in the ordergiven; and irradiating the laminate with laser light for thoroughlycutting the laminate (full cut). In the case of full cut, an irradiationdirection of laser light may be changed in accordance with the kind andthe like of a layer to be formed. In this way, a cutting depth isadjusted, and thus a desired impact-absorbing pressure-sensitiveadhesive sheet may be obtained.

In the case of half cut and the case of full cut, cutting is preferablyconducted so that a distance between cut surfaces of the adjacentimpact-absorbing pressure-sensitive adhesive layers is 30 μm or more.That is, in the case of half cut, cutting is preferably conducted sothat the distance L2 between a side surface lower end 11 b and a sidesurface lower end 11 b of the adjacent impact-absorbingpressure-sensitive adhesive pieces is 30 μm or more, more preferably 30to 120 μm, and particularly preferably 30 to 60 μm. Thus, re-adhesion ofthe cut surfaces maybe prevented, and excellent operability duringlamination to an optical device may be obtained. Further, excellentyield may be obtained. The distance between the cut surfaces is adjustedwithin the above ranges, and thus the obtained impact-absorbingpressure-sensitive adhesive sheet may have excellent releasability fromthe substrate and excellent operability during lamination to an opticaldevice. Further, re-adhesion of the adjacent cut surfaces may beprevented, the tapered surfaces are favorably maintained, and excellentdisplay properties of an image display apparatus may be provided.Meanwhile, excellent yield may be obtained.

The laser light preferably includes light having a wavelength of atleast 400 nm or less and/or 1.5 μm or more, more preferably 2 to 30 μm,and particularly preferably 8 to 12 μm. Thus, a material used forforming each layer (film) such as the impact-absorbingpressure-sensitive adhesive layer may efficiently absorb laser light andmay be cut favorably. As a result, the desired taper angle and distancebetween side surfaces (cut surfaces) may easily be attained.

The laser may employ any appropriate laser. Specific examples thereofinclude: gas laser such as CO₂ laser or excimer laser; solid laser suchas YAG laser; and semiconductor laser. CO₂ laser is preferred becausethe CO₂ laser light may include light having preferred wavelengths.Further, the CO₂ laser has a wide applicable range of irradiation outputconditions, allows easy control of the cutting depth, easily satisfiesthe desired taper angle, and provides excellent cut surfaces. Further,the CO₂ laser easily provides the distance between the cut surfaces,suppresses re-adhesion of the cut surfaces, and provides excellentproductivity.

Irradiation conditions of laser light (for example, output conditions,transfer rate, and number of irradiation) may employ any appropriateconditions in accordance with a cutting target, a cutting depth, and thelike. In the case where CO₂ laser is used, the output conditions are 10to 800 W, preferably 10 to 200 W, and more preferably 10 to 100 W. Inthe case where CO₂ laser is used, the transfer rate is typically 50 to700 mm/second, and preferably 100 to 500 mm/second. The number ofirradiation is typically once or twice.

G. Use Method

A method of using an impact-absorbing pressure-sensitive adhesive sheetof the present invention may employ any appropriate method. A typicalexample of the method involves peeling the substrate (separator) andattaching the peeled surface to a surface of an optical device.

EXAMPLES

Hereinafter, the present invention will be described more specificallyby way of examples, but the present invention is not limited to theexamples. Note that parts and % in examples refer to parts by weight andwt % unless otherwise noted.

Production Example 1 Production of Impact-Absorbing Layer

Into a reaction vessel equipped with a condenser, a nitrogenintroduction pipe, a thermometer, a UV irradiation device, and astirring device, 83.6 parts of 2-ethylhexyl acrylate, 16.4 parts of4-hydroxybutyl acrylate, and 0.05 part of2,2-dimethoxy-2-phenylacetophenone (“Irgacure-651”, available from CibaSpeciality Chemicals) and 0.05 part of 1-cyclohexylphenyl ketone(“Irgacure Ir-184”, available from Ciba Speciality Chemicals) as aphotopolymerization initiator were charged. The mixture was irradiatedwith UV light for polymerization, and an acrylic polymer/monomer mixedliquid having a polymerization rate of 10% was obtained. Next, into 100parts of this mixed liquid, 0.2 part of trimethylpropane triacrylate asa crosslinking agent and 0.15 part of 1-hydroxycyclohexylphenyl ketone(“Irgacure Ir-184”, available from Ciba Speciality Chemicals) as aphotopolymerization initiator were mixed, to thereby obtain anapplication liquid.

The application liquid obtained above was applied onto a substrate(polyester-based separator having a thickness of 100 μm, “PET SEPA MRF”,available from Mitsubishi Polyester Film Corporation), and an uppersurface thereof was covered with a substrate having lower peel forcethan that of the substrate (polyester-based separator having a thicknessof 75 μm, “PET SEPA MRN”, available from Mitsubishi Polyester FilmCorporation), to thereby obtain a laminate. The obtained laminate wasirradiated with UV light at 4,000 mJ/cm² by using a UV lamp undercooling at −15° C. for photopolymerization, to thereby obtain animpact-absorbing layer having a thickness of 204 μm. A dynamic storagemodulus G′ of the obtained impact-absorbing layer at 20° C. was 1×10⁵Pa.

Production Example 2 Production of Undercoat Layer

Into a four-necked flask equipped with a condenser, a stirring blade,and a thermometer, a solution prepared by mixing 100 parts of butylacrylate, 5 parts of acrylic acid, 0.1 part of 4-hydroxybutyl acrylate,and 0.2 part of benzoyl peroxide with 100 parts of ethyl acetate wasadded for a reaction at 60° C. for 7 hours, to thereby obtain a solutionof an acrylic polymer having a solid content of 40%. To 100 parts of theacrylic polymer solution in solid content, 1 part of an isocyanate-basedcompound in solid content (Coronate L, available from NipponPolyurethane Industry Co., Ltd.) was added, and ethyl acetate was added,to thereby prepare an undercoat solution having a solid content of 30%.The obtained undercoat solution was applied onto a substrate(polyester-based separator having a thickness of 38 μm) by a reverseroll coat method, and the whole was dried at 150° C. for 3 minutes forevaporation of a solvent, to thereby produce an undercoat layer. Athickness of the obtained undercoat layer after drying was 23 μm.

Example 1

The substrate (“PET SEPA MRN”) on one side of the impact-absorbing layerobtained above was peeled off, and the undercoat layer obtained aboveand a first separator (substrate) were laminated to this peeled surfacein the order given. Next, the substrate (“PET SEPA MRF”) on another sideof the impact-absorbing layer was peeled off, and the undercoat layerobtained above and a second separator were laminated to this peeledsurface in the order given. A PET film (trade name “MDAR”, availablefrom Toyo Metallizing Co., Ltd.) having a thickness of 75 μm was used asthe first separator. A PET film (polyester film, trade name “MRV”,available from Mitsubishi Polyester Film Corporation) having a thicknessof 75 μm was used as the second separator. In this way, a laminate Ahaving a structure of first separator (75 μm)/impact-absorbingpressure-sensitive adhesive layer (250 μm)/second separator (75 μm) wasproduced.

The laminate A obtained above was irradiated with laser light from CO₂laser (trade name “SILAS-SAM (SPL2305 type)”, manufactured by ShibuyaKogyo Co., Ltd.), and the second separator and the impact-absorbingpressure-sensitive adhesive layer were cut (half cut), to therebyproduce the impact-absorbing pressure-sensitive adhesive sheet as shownin FIG. 2A. Dimensions of the obtained impact-absorbingpressure-sensitive adhesive piece were 40 mm in length×30 mm in width.Cutting by laser light was conducted under the conditions of: an outputof 50 W; a transfer rate of 400 mm/second; a focus of 66 mm; and thenumber of irradiation of once. Note that the focus refers to a distancefrom an outermost surface of a lens of laser to a surface of thelaminate (second separator).

Example 2

An impact-absorbing pressure-sensitive adhesive sheet was produced inthe same manner as in Example 1 except that: the focus was changed to 64mm.

Example 3

An impact-absorbing pressure-sensitive adhesive sheet was produced inthe same manner as in Example 1 except that: the output was changed to25 W; and the transfer rate was changed to 200 mm/second.

Example 4

An impact-absorbing pressure-sensitive adhesive sheet was produced inthe same manner as in Example 1 except that: the output was changed to25 W; the transfer rate was changed to 200 mm/second; and the focus waschanged to 64 mm.

Example 5

An impact-absorbing pressure-sensitive adhesive sheet was produced inthe same manner as in Example 1 except that: the output was changed to25 W; the transfer rate was changed to 200 mm/second; and the focus waschanged to 62 mm.

Example 6

The substrate (“PET SEPA MRN”) on one side of the impact-absorbing layerobtained above was peeled off, and the undercoat layer obtained above, apolarizing plate (trade name, TEG1465DUHC, available from Nitto DenkoCorporation) having a thickness of 100 μm, the undercoat layer obtainedabove, and a first separator (substrate) were laminated to this peeledsurface in the order given. Next, the substrate (“PET SEPA MRF”) onanother side of the impact-absorbing layer was peeled off, and theundercoat layer obtained above and a second separator were laminated tothis peeled surface in the order given. The same separators as those ofExample 1 were used as the first separator and the second separator,respectively. In this way, a laminate B having a structure of firstseparator (75 μm)/pressure-sensitive adhesive layer (23 μm) /polarizingplate (100 μm) /impact-absorbing pressure-sensitive adhesive layer (250μm)/second separator (75 μm) was produced.

The laminate B obtained above was irradiated with laser light from CO₂laser, and the second separator, the impact-absorbing pressure-sensitiveadhesive layer, the polarizing plate, and the pressure-sensitiveadhesive layer were cut (half cut), to thereby produce theimpact-absorbing pressure-sensitive adhesive sheet as shown in FIG. 2B.Dimensions of the obtained impact-absorbing pressure-sensitive adhesivepiece were 40 mm in length×30 mm in width. Cutting by laser light wasconducted under the conditions of: an output of 75 W; a transfer rate of400 mm/second; a focus of 66 mm; and the number of irradiation of once.

Example 7

The substrate (“PET SEPA MRN”) on one side of the impact-absorbing layerobtained above was peeled off, and the undercoat layer obtained above, asupport layer, the undercoat layer obtained above, and a separator(substrate) were laminated to this peeled surface in the order given.Next, the substrate (“PET SEPA MRF”) on another side of theimpact-absorbing layer was peeled off, and the undercoat layer obtainedabove and a polarizing plate (trade name, TEG1465DUHC, available fromNitto Denko Corporation) were laminated to this peeled surface in theorder given. A PET film (trade name “MDAR”, available from ToyoMetallizing Co., Ltd.) having a thickness of 75 μm was used as theseparator. A film exerting substantial optical isotropic property(thickness of 60 μm, dynamic storage modulus G′ of 2×10⁹ Pa, Δnd[590]=5nm, Rth[590]=7 nm, trade name: Zeonor ZF-14, available from ZeonCorporation) was used as the support layer. In this way, a laminate Chaving a structure of separator (75 μm)/pressure-sensitive adhesivelayer (23 μm)/support layer (60 μm)/impact-absorbing pressure-sensitiveadhesive layer (250 μm)/polarizing plate (100 μm) was produced.

The laminate C obtained above was irradiated with laser light from CO₂laser, and the laminate C was cut (full cut), to thereby produce theimpact-absorbing pressure-sensitive adhesive sheet as shown in FIG. 1C.Dimensions of an impact-absorbing pressure-sensitive layer of theimpact-absorbing pressure-sensitive adhesive sheet were 40 mm inlength×30 mm in width. Cutting by laser light was conducted under theconditions of: an output of 100 W; a transfer rate of 400 mm/second; afocus of 66 mm; and the number of irradiation of once.

Comparative Example 1

An impact-absorbing pressure-sensitive adhesive sheet was produced inthe same manner as in Example 1 except that: laser light was irradiatedby using UV laser (trade name “5330”, manufactured by Electro ScientificIndustries, Inc.); the output was changed to 20 W; and the transfer ratewas changed to 2 mm/second.

Comparative Example 2

An impact-absorbing pressure-sensitive adhesive sheet was produced inthe same manner as in Example 1 except that cutting was conducted byusing a continuous automatic cutting machine (Super cutter, a tip angleof 45°, double edge).

Comparative Example 3

An impact-absorbing pressure-sensitive adhesive sheet was produced inthe same manner as in Example 1 except that cutting was conducted by awater jet method. Note that the cutting conditions were: a waterextrusion pressure of 350 MPa; a tip diameter (water extrusion diameter)of Φ0.1 mm, and a transfer rate of 2 mm/second.

Table 1 collectively shows the impact-absorbing pressure-sensitiveadhesive sheets obtained in Examples and Comparative Examples. Note thatthe obtained impact-absorbing pressure-sensitive adhesive sheets wereevaluated by the following method.

1. Measurement of Taper Angle

For Examples 1 to 5

The taper angle was calculated from a value obtained by measuring anextended width (L6 in FIG. 2A) of the impact-absorbingpressure-sensitive adhesive piece from the second separator and a total(325 μm) of the thickness of the impact-absorbing pressure-sensitiveadhesive piece and the thickness of the second separator.

For Example 6

The taper angle was calculated from a value obtained by measuring anextended width (L7 in FIG. 2B) of the pressure-sensitive adhesive layerfrom the second separator and a total (448 μm) of the thickness of thepressure-sensitive adhesive layer, the thickness of polarizing plate,the thickness of the impact-absorbing pressure-sensitive adhesive piece,and the thickness of the second separator.

For Example 7

The taper angle was calculated from a value obtained by measuring anextended width (L8 in FIG. 1C) of the separator from the polarizingplate and a total (508 μm) of the thickness of the separator, thethickness of the pressure-sensitive adhesive layer, the thickness of thesupport layer, the thickness of the impact-absorbing pressure-sensitiveadhesive piece, and the thickness of the polarizing plate.

2. Evaluation of Cut Surface

The cut surface (side surface) of the impact-absorbingpressure-sensitive adhesive layer (impact-absorbing pressure-sensitiveadhesive piece) was observed with a microscope.

Evaluation Results

-   ∘: Smooth-   x: Wavy, uneven, etc.    3. Re-Adhesion

Whether the adjacent impact-absorbing pressure-sensitive adhesive layers(impact-absorbing pressure-sensitive adhesive pieces) re-adhered duringor after cutting was observed.

Evaluation Results

-   ∘: No re-adhesion observed-   x: Re-adhesion observed    4. Evaluation of Releasability

The separator (substrate) was peeled off from each of tenimpact-absorbing pressure-sensitive adhesive sheet or impact-absorbingpressure-sensitive adhesive pieces obtained. During peeling, ease ofpeeling, and the presence or absence of adhesive defects (partialattaching of the impact-absorbing pressure-sensitive adhesive layer(impact-absorbing pressure-sensitive adhesive piece) to the separator)were evaluated.

Evaluation Results

-   ∘: Excellent releasability-   x: Poor releasability

TABLE 1 L6 Taper L3 (L7, L8) Thickness angle L2 L5 (L4) ReleasabilityProductivity (μm) (μm) (°) (μm) (μm) (μm) Cut surface Readhesion ∘ x(Chips/h) Example 1 40 325 83 80 — 160 ∘ ∘ 10 0 9000 Example 2 60 325 8040 — 160 ∘ ∘ 10 0 9000 Example 3 80 325 76 30 — 190 ∘ ∘ 10 0 4500Example 4 100 325 73 30 — 230 ∘ ∘ 6 4 4500 Example 5 140 325 67 30 — 310∘ ∘ 9 1 4500 Example 6 60 448 83 45 40 160 ∘ ∘ 10 0 9000 Example 7 70508 82 — — — ∘ ∘ 10 0 9000 Comparative — 325 — — — 70 Δ Δ 5 5 45 example1 Comparative — 325 90 — — 0 x x — — 8000 example 2 Comparative — 325 —— — — x x — — 350 example 3

Table 1 reveals that the impact-absorbing pressure-sensitive adhesivesheets of Examples 1 to 7 each had a taper angle of 65° or more andexcellent yield. Further, the impact-absorbing pressure-sensitiveadhesive sheets each had a smooth cut surface with a tapered surface.Meanwhile, the impact-absorbing pressure-sensitive adhesive sheet ofComparative Example 1 had nearly smooth surface. However, the sidesurface lower ends of the adjacent impact-absorbing pressure-sensitiveadhesive pieces re-adhered, and no tapered surface was formed. Thus, notaper angle was measured. The impact-absorbing pressure-sensitiveadhesive sheet of Comparative Example 2 had a taper angle ofsubstantially 90°, but the adjacent impact-absorbing pressure-sensitiveadhesive pieces re-adhered. In Comparative Example 3, no half cut(cutting of the second separator and the impact-absorbingpressure-sensitive adhesive layer only) was realized, which resulted infull cut (cutting of the first separator as well). Further, the cutsurfaces re-adhered, and thus no taper angle was measured. In theimpact-absorbing pressure-sensitive adhesive sheets of ComparativeExamples 2 and 3, the cut surfaces re-adhered, and no tapered surfacewas formed.

The impact-absorbing pressure-sensitive adhesive sheets of Examples 1 to3 and Examples 6 and 7 each had excellent releasability. In theimpact-absorbing pressure-sensitive adhesive sheet of each of Examples 4and 5 having a relatively small taper angle, the impact-absorbingpressure-sensitive adhesive piece and the second separator in some ofthe sheets were integrated and were not peeled, and the second separatoralone was peeled off. Comparative Example 1 involved re-adhesion asdescribed above. Thus, peeling involved difficulties, and adhesivedefects were caused. Releasability was poor. In Comparative Examples 2and 3, re-adhesion of the cut surfaces was extensive and noreleasability was evaluated. Note that the impact-absorbingpressure-sensitive adhesive sheets of examples excluding ComparativeExamples 1 and 3 each had excellent productivity. In particular, theimpact-absorbing pressure-sensitive adhesive sheets of Examples 1 and 2and Examples 6 and 7 each had excellent productivity.

The impact-absorbing pressure-sensitive adhesive piece obtained in eachof Example 1 and Comparative Example 1 was used in an image display partof a cell phone. As a result, the impact-absorbing pressure-sensitiveadhesive piece of Example 1 provided excellent viewing properties thanthose of Comparative Example 1.

The impact-absorbing pressure-sensitive adhesive sheet of the presentinvention may suitably be used for an image display apparatus such as aliquid crystal display apparatus.

Many other modifications will be apparent to and be readily practiced bythose skilled in the art without departing from the scope and spirit ofthe invention. It should therefore be understood that the scope of theappended claims is not intended to be limited by the details of thedescription but should rather be broadly construed.

What is claimed is:
 1. An impact-absorbing pressure-sensitive adhesivesheet comprising: a separator; and an impact-absorbingpressure-sensitive adhesive layer including an impact-absorbing layerand provided on one side of the separator, wherein: the separator isreleasable from the impact-absorbing pressure-sensitive adhesive layer,the separator has an exposed side edge or side surface which extends ina direction along an edge of a side surface of the impact-absorbingpressure-sensitive adhesive layer; the side surface of the entireimpact-absorbing pressure-sensitive adhesive layer includes a taperedsurface; and the tapered surface has a taper angle of 65° or more.
 2. Animpact-absorbing pressure-sensitive adhesive sheet according to claim 1,wherein the impact-absorbing layer has a thickness of 100 to 1,000 μm.3. An impact-absorbing pressure-sensitive adhesive sheet according toclaim 1, wherein the impact-absorbing layer has a dynamic storagemodulus G′ of 1×10⁷ Pa or less at 20° C.
 4. An impact-absorbingpressure-sensitive adhesive sheet comprising: a separator; and aplurality of impact-absorbing pressure-sensitive adhesive pieces eachincluding an impact-absorbing layer and provided at certain intervals onone side of the separator, wherein: a side surface of each of the entireimpact-absorbing pressure-sensitive adhesive pieces includes a taperedsurface; and the tapered surface has a taper angle of 65° or morewherein the impact-absorbing layer has a thickness of 10 to 1,000 μm. 5.An impact-absorbing pressure-sensitive adhesive sheet according to claim4, wherein: the plurality of impact-absorbing pressure-sensitiveadhesive pieces are provided at certain intervals on one side of theseparator; and a distance between side surface lower ends of theadjacent impact-absorbing pressure-sensitive adhesive pieces is 30 μm ormore.
 6. An impact-absorbing pressure-sensitive adhesive sheet accordingto claim 4, wherein the impact-absorbing layer has a dynamic storagemodulus G′ of 1×10⁷ Pa or less at 20° C.
 7. An impact-absorbingpressure-sensitive adhesive sheet, wherein the impact-absorbingpressure-sensitive adhesive sheet is obtained by thoroughly cutting alaminate comprising a separator and an impact-absorbingpressure-sensitive adhesive layer including an impact-absorbing layerand provided on one side of the separator, whereby the impact-absorbingpressure-sensitive adhesive layer has a thoroughly-cut side end surface,the thoroughly-cut side end surface of the entire impact-absorbingpressure-sensitive adhesive layer is a tapered surface; and the taperedsurface has a taper angle of 65° or more.